The present invention relates to interferometers, and more particularly to an interferometric system capable of measuring rate changes in response to piezoelectric movement.
In new generation aircraft, various sensors and systems are used to control all phases of aircraft operation from takeoff to landing. Much sophisticated technology has been employed to develop new instrumentation and the new techniques and systems have been applied to commercial aircraft as well as to the operation and control of missiles and other space vehicles. These new instruments have been used to replace prior art electromechanical devices such as mechanical gyroscopes, acceleration and rate sensors, and other elements of inertial attitude and heading reference systems.
With the advent of laser technology, intensive research revealed that many of the guidance and sensor systems could be increased in accuracy by employment of devices utilizing the characteristics of the lasers. In particular, extensive studies have been made concerning the development of laser gyros which may enable the construction of highly precise and computer controlled guidance systems without the normal deficiencies caused by the size and weight requirements of prior art electromechanical devices. While new instruments have been developed, the relatively new technology has not yet proven to be reliable and accordingly has not been shown to be commercially acceptable in most environments and applications.
While the technology continues to develop with respect to laser operated instruments, other alternatives employing the piezoelectric technology have been developed for commercial application. In one example of a prior known navigation system employing a strapped-down inertial technique, as disclosed in co-pending U.S. patent application Ser. No. 370,641 entitled "Sensor Assembly for Strapped-Down Attitude and Heading Reference System" by B. F. Rider, filed Apr. 21, 1982 and assigned to the same assignee as this application, U.S. Pat. No. 4,444,053 a rotating rate and acceleration sensor employing piezoelectric devices is disclosed which provides rate and acceleration measurement in multiple axes. Signal outputs from this rotating sensor are used to provide the rate and acceleration signals utilized in the navigation and control of an aircraft. Although the construction of the aforementioned system has substantially reduced the cost and complexity of the assembly necessary for providing improved signal processing capabilities, there is still significant complex circuitry required for coupling and demodulating the signals representing rate and acceleration. These circuits do not completely eliminate all problems caused hy harmonics, noise, phase shift and misalignment errors encountered during operation of the system.
In other prior known techniques employing similar rotating piezoelectric sensors, alternative structures have been suggested. In one such system disclosed in a co-pending U.S. patent application entitled "Multisensor Demodulator and A/D Converter" by Wilmer A. Mickelson, filed on Oct. 5, 1982, and assigned to the same assignee as this application, the analog signals from a rotating sensor are directly converted to digital signals for reducing the complexity of the signal processing circuitry required to produce accurate representations of rate and acceleration measurements. Again, signals developed by rotating piezoelectric sensors sense the components of rate and acceleration to which an aircraft is exposed during roll, pitch, and yaw changes in flight and these signals are directly converted to digital representations used to provide aircraft navigation and control.
Although each of the mentioned systems attempts to minimize the number of electrical components, cost and weight of the system, while improving accuracy and repair rates, there is still a continuing need to further reduce the complexity of the structure. Significant developments associated with the inherent characteristics of the laser have shown that optical gyroscopes and similar devices may provide certain benefits in some areas at the expense of cost and uncertainty in other areas. However, the technology is promising and research continues to define more applications, systems and structures that will enable use of the laser.
Accordingly, the present invention has been developed to make use of the evolving laser technology in connection with a piezoelectric sensor to produce a system capable of providing accurate, lightweight, and reliable interferometric measurements useful for determinations of rate, acceleration, and other parameters.